I'm at Beagle Point and have have fired off 2 my 3 Heatsinks (but have 2 left thanks to a bug before 2.1)
The first one got fired at random without my knowledge - I just started the game and noticed I only had two. Eventually tracked down the binding (V iirc) and disabled it - most likely it was fired instead of zero'ing throttle.
The 2nd one I fired at Cmdr Dognosh during one of our chats

A couple of thousand ly out and I fumbled over the keyboard - the first I knew was the heat dropping like a stone and I'm panicking thinking my engines are going offline!
To balance that view though, on my first run out, I hit a bunch of Neutrons and used a heat sink in anger to escape the gravitational lock one had over my ship (T6 at the time). On this run (in an Asp) I've jumped into a few binaries that have put me in the corona of both - I come barreling in on full throttle and seemed to have the momentum to escape with only minor 'fizzing' so no HS fired......yet